Impedance matching in radio frequency transmission lines may be accomplished in many different ways:
1. Lumped Elements—An L-C circuit using capacitors and inductors, is not usually seen above about 150 MHz.
2. Two and Three Stub Tuners—Two or three transmission line “stubs” are connected along the transmission line to be matched. The stubs each have a sliding short. The positions of the short are adjusted to have a matching effect. This has the disadvantages of being difficult to manufacture, has obscure interaction between the two or three adjustments, and having noisy sliding contacts.
3. Air line with dielectric slugs—A coaxial air line of nominal impedance (typically 50 Ohms) has two sliding slugs of dielectric material, sometimes with metal loading to increase the equivalent dielectric constant. Each slug is approximately a quarter wavelength long in the transmission line, producing a movable section of lower impedance (Z) line. When the two slugs are in contact, they form a half wavelength of low Z line, which has no transforming effect. A transforming effect is formed as the slugs move apart and the spaced pair is moved along the transmission line. This is relatively easy to adjust and has very low noise, because of having no physical sliding contacts. However, it is relatively hard to manufacture, and of relatively narrow band.
U.S. Pat. No. 4,754,239 discloses a waveguide to stripline transition assembly. Impedance matching is determined by adjusting a reflecting panel behind a tapered wedge. U.S. Pat. No. 4,754,239 is hereby incorporated by reference into the specification of the present invention.
U.S. Pat. No. 4,785,266 discloses a wedge shaped dielectric rod polarizer for microwave communication systems. The device imparts a phase shift on circularly polarized radiation at the wedge, so linearly polarized radiation exits the device. The device does not provide impedance matching along a transmission line. The present invention is not limited in this regard. U.S. Pat. No. 4,785,266 is hereby incorporated by reference into the specification of the present invention.
U.S. Pat. No. 6,653,911 discloses an integrated circuit apparatus for impedance matching. At least one stripline is sandwiched between two dielectric materials. The dielectric material is spaced a distance from a ground plane. A series of stripline segments are connected together, with the distance between the striplines and the ground plane selected for impedance matching. The thickness of the dielectric material varies, and is different than the thickness of the dielectric material in adjacent stripline sections resulting in a different distance between the stripline and the ground plane. The present invention is not limited in either regard. U.S. Pat. No. 6,653,911 is hereby incorporated by reference into the specification of the present invention.
U.S. Pat. No. 6,717,965 discloses a tapered interference filter for tuning a laser. A graded thin film is used as a channel selector. The device does not provide impedance matching along a transmission line. The present invention is not limited in this regard. U.S. Pat. No. 6,717,965 is hereby incorporated by reference into the specification of the present invention.
Known non-patent publications include:
Microwave Transmission Circuits, George L. Ragan ed., Boston Technical Publishers, Inc., 1964, pp.456-481;
Very High-Frequency Techniques, Herbert J. Reich ed., McGraw-Hill Book Company, Inc., 1947, pp. 794-795; and
2001 ARRL Handbook for Radio Amateurs, Chuck Hutchinson ed., American Radio Relay League, pp. 19.10-19.17 and 20.50-20.51.